This invention relates to novel collector compositions useful for the recovery of metal-containing minerals from mineral ores by froth flotation.
Flotation is a process of treating a mixture of finely divided mineral solids, e.g., a pulverulent ore, suspended in a liquid whereby a portion of such solids is separated from other finely divided mineral solids, e.g., clays and other like materials, present in the ore by introducing a gas (or providing a gas in situ) in the liquid to produce a frothy mass containing certain of the solids on the top of the liquid, and leaving suspended (unfrothed) other solid components of the ore. Flotation is based on the principle that introducing a gas into a liquid containing solid particles of different materials suspended therein causes the selective adherence of some gas to certain suspended solids and not to others and makes the particles having the gas thus adhered thereto lighter than the liquid. Accordingly, these particles rise to the top of the liquid to form a froth.
Various flotation agents have been admixed with the suspension to improve the frothing and collection process. These agents are classed according to the function to be performed and include collectors such as xanthates, thionocarbamates and the like; frothers which facilitate the forming of a stable froth such as natural oils, e.g., pine oil and eucalyptus oil; modifiers such as activators, e.g., copper sulfate, to induce flotation in the presence of a collector; depressants, e.g., sodium cyanide, which tend to prevent a collector from functioning as such on a mineral which it is desired to retain in the liquid and thereby discourage a substance from being carried up and forming a part of the froth; pH regulators, e.g., lime and soda ash, to produce optimum metallurgical results; and the like.
The phenomena which renders flotation a particularly valuable industrial operation appear to be largely associated with selective affinity of the surface of particulated solids, suspended in a liquid containing entrapped gas, for the liquid on the one hand, the gas on the other. The specific additives used in a flotation operation are selected according to the nature of the ore, the mineral sought to be recovered and the other additives which are to be used in combination therewith.
Flotation is employed in a number of mineral separation processes including the selective separation of such metal-containing sulfide minerals such as those containing copper, zinc, lead, nickel, molybdenum and other metals from iron-containing sulfide minerals such as pyrite or pyrrhotite.
Once recovered, the metal-containing minerals are converted to the more useful pure metal state, often by a smelting process. Such smelting processes can result in the formation of volatile sulfur compounds. These volatile sulfur compounds are often released to the atmosphere through smokestacks, or are removed from such smokestacks by expensive and elaborate scrubbing equipment.
Among collectors commonly used for the recovery of metal-containing sulfide minerals or sulfidized metal-containing oxide minerals are xanthates, dithiophosphates and thionocarbamates. Unfortunately, these materials are not particularly selective in the recovery of sulfide or sulfidized oxide minerals. For example, many nonferrous metal-containing sulfide minerals are found naturally in ore which also consists of iron-containing sulfide minerals when the iron-containing sulfide minerals are recovered in flotation processes along with the nonferrous metal-containing sulfide minerals and sulfidized metal-containing oxide minerals, there is excess sulfur present which is released in the smelting processes resulting in an undesirably high amount of sulfur present during the smelting operations. The xanthates, thionocarbamates and dithiophosphates do not selectively recover nonferrous metal-containing sulfide minerals in the presence of iron-containing sulfide minerals. On the contrary, such collectors collect and recover all metal-containing sulfide minerals.
Other collectors commonly recognized as useful in the recovery of sulfide-containing metal or sulfidized metal oxide values are mercaptans, disulfides (R--SS--R) and polysulfides (R--(S).sub.n --R), wherein n is 3 or greater. Unfortunately, the mercaptan collectors have an environmentally undesirable odor, and are very slow kinetically in the flotation of metal sulfides. The disulfides and polysulfides, when used as collectors, give low recoveries with slow kinetics. Furthermore, the mercaptans, disulfides and polysulfides do not selectively recover nonferrous metal sulfides in the presence of ferrous sulfides.
In view of the foregoing, a composition which is useful for the recovery, at relatively good recovery rates and selectivity, of a broad range of metal-containing minerals from mineral ores, including metal-containing sulfide minerals, sulfidized metal-containing oxide minerals and metal-containing oxide minerals is desired.